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I've noticed that when a WiFi system is set up on an aircraft, a small bulbous structure is added. What does it contain and how does this WiFi system work?

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The small bulb houses the antenna that provides the satellite communications for the internet link.

Inside the aircraft several wireless access points provide a WIFI signal to the passenger's equipment. The wireless access points are connected to a central modem which in turn is connected to the transceiver unit. The transceiver uses the rooftop antenna to communicate to a geostationary satellite.

aircraft satellite antenna

source: dailywireless

MELCO antenna

source: Flightglobal

The antenna is a small dish or phased array that is aimed at the communication satellite using servo motors and/or electronic beam steering. The antenna control system receives information about the position and attitude of the aircraft to calculate the relative position to the geostationary satellites that provides the internet communications signal.

There are also systems available on the market that use a ground based network to communicate with the internet. These systems cannot provide global coverage since the aircraft needs to be in line of radio sight of a ground based antenna.

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    $\begingroup$ Wow, phased array... It's only thanks to your post that I can fully appreciate the simplest thing like a normal wifi conncetion I'm used to get all over the place. $\endgroup$
    – Pavel
    May 19, 2015 at 16:35
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    $\begingroup$ The wifi connection (link between your device and the wifi router in the airplane) is pretty conventional, in the exact same manner as the wifi connection in your home or a cafe. The pictured device and antenna are for the internet connection between the airplane and the rest of the world - replacing the cable or fiber optic connection that you or the cafe might have to your internet service provider. $\endgroup$
    – Peteris
    May 19, 2015 at 21:07
  • $\begingroup$ Possibly Pavel is confused about the difference between Wi-Fi and the Internet? $\endgroup$
    – user253751
    May 20, 2015 at 6:24
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    $\begingroup$ @immibis: I just didn't make myself crystal clear, that's all. I used to work in wireless network business (where I got the feeling of omnipresent wireless connection to the Internet) as well as non-destructive material testing, where I got to appreciate the technical and computational complexity of phased array. I have yet to get to building and launching a communication satellite, though. $\endgroup$
    – Pavel
    May 20, 2015 at 7:59
  • $\begingroup$ While I see the image from Lufthansa above. They turn off the WiFi called "Fly-Net" above mainland China, beause "free as in free speech" ist not available above China. However, I'm glad that it is not allowed to make calls during flight and being not available is a pleasure. $\endgroup$
    – Peter
    Feb 12, 2016 at 10:42

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